1. Field of the Invention
The present invention relates to a developing apparatus which is used for electrophotographic type copy machine and printer. More particularly, the present invention relates to a developing apparatus wherein both the developer to be carried onto a developer carrier supplied from a developer supply portion and the developer present in a developer tank surely circulate so that the developing apparatus can obtain appropriate pressure of developer.
2. Description of the Prior Art
A known conventional developing apparatus used for electrophotographic type copy machine and printer is such that non-magnetic one-component developer not including carrier is used and the developer is supplied onto a developer carrier and forms thin layer of developer on the developer carrier before development.
An example of such a conventional developing apparatus is shown in FIG. 12. In a developing apparatus 100, a toner hopper 106 for accommodating developer is arranged at a position lower than a position where a development sleeve 103 is rotatably installed. The developing apparatus 100 has: a supply roller 104 for supplying developer, i.e., toner, to the development sleeve 103; and a stirring member 107 for stirring toner present in the toner hopper 106. A regulating blade 102 is made to press periphery of the development sleeve 103. The regulating blade 102 is provided so as to make thickness of thin layer of toner to be formed on the development sleeve 103 uniform and make toner negatively charged.
In the developing apparatus 100, the supply roller 104 supplies toner to the development sleeve 103. Next, the toner supplied to the developing sleeve 103 is regulated by the regulating blade 102, then carried onto the development sleeve 103 in a thin layer state. After that, the thin layer of toner gets electrostatic latent images on a photosensitive drum 90 developed. On the other hand, toner not carried onto the development sleeve 103 is returned to the toner hopper 106 and mixed with toner present in the toner hopper 106.
However, in the development apparatus 100, a developer supply portion for supplying developer to the development sleeve 103 can collect a little amount of toner. Since the toner hopper 106 is arranged at a position lower than the position of the development sleeve 103, toner has to be drawn up from the toner hopper 106 to supply to the development sleeve 103. Thereby, there has been a problem that pressure of toner applied to the development sleeve 103 gets low because weight of toner is too light to generate appropriate pressure. When the pressure of toner is low, the development sleeve 103 can take a little toner through the regulating blade 102 and as a result, the deterioration of toner-taking condition at the development sleeve 103 causes following deterioration on a high-density image at a large area, or the like.
Different from the developing apparatus 100, there has been a conventional developing apparatus wherein a toner hopper is arranged above a development sleeve.
Such a conventional developing apparatus does not have a following-deterioration kind problem. However, there has been a problem that the toner present at a developer supply portion and the toner present in a toner hopper do not circulate well. That is, since the toner hopper is arranged at a position higher than the position of the development sleeve, the developer supply portion is covered with toner and pressure of toner applied thereto becomes high. Thereby, the following problems have occurred to the conventional developing apparatus: same toner particles repeatedly receive stress by regulation of a regulating blade and then, the stress causes the toner particles to crack; the cracked tiny powder of toner melts and adheres to the development sleeve; or the regulating blade gets stiff because of cracked toner adhering thereto, whereby image quality deteriorates.
As described, in conventional developing apparatus, pressure of developer applied at a regulating position where a regulating member regulates developer is not constant. Thereby, there have been inconveniences: following deterioration on a high-density image occurs due to deterioration of toner-taking condition at a development sleeve when the pressure of developer is insufficient; or developer present at the regulating position adheres thereto when the pressure of developer is too high.